Calling HAMs or Sparks: Signal Loss Through Coax


#1

I’m looking for some advice regarding my setup. After significant efforts to finally raise my antenna to its final height of 47’, I now have reduced range and message counts relative to my previous setup. Let me explain.

Previous Setup
FA Antenna -> N-to-SO239 Adapter -> 50’ Low-Loss RG8 Coax -> 6” SO239-to-SMA Cable -> FA Prostick Plus

I have a 40’ tower and had the antenna mounted at around 35’. The rPi was mounted in an outdoor enclosure near the base and a “long-term temporary” 100’ Cat5 cable ran back to the router. The Pi was too far from the WAP to use WiFi.

This setup yielded around 2,000 aircraft with 400,000 positions daily, 24% of which were from 80+ nm away.
Over time, the Florida heat and humid air killed a rPi (or two). After damage to the Cat5 cable killed the enet port on another Pi, I decided it was time to relocate it indoors.

”Improved” Setup
I fabricated a new mast with proper lightning protection and nice, proper antenna mounts. Extending above the top of the tower, it puts the FA antenna at about 47’. I had to add another 50’ length of RG8 and a SO239 butt connector in order to reach the Pi, now indoors.

I’m now seeing 1,750 aircraft daily, with only 220,000 positions, only 7% of which are from 80+ nm away. In short, I now have much reduced range.

Bottom Line
I’m frustrated that having finally completed my setup, I now have worse results. Aside from the fact that it looks great, with the new mast and all, the 12’ height increase brings an order of magnitude improvement in line-of-sight/reduced obstacles. To troubleshoot I grabbed a 50’ extrension cord and moved the Pi outside to connect it at the end of the first 50’ length of coax. That seemed to help, but puts me in the situation of having the Pi back outside, which never ends well in Florida. Can the extra length of RG8 really cause that much signal loss? How much loss can be attributed to the butt connector? Any ideas on how to work around this?


#2

too long cable.

Neede LNA .
FA Antenna ->LNA-> cable -> FA Prostick Plus

An additional issue is perhaps a powerful source of interference. -


#3

SO239 (AKA UHF) connectors are not suggested for use above 300 Mhz, per their manufacturer. Granted, that’s for transmitting, but loss is loss, either way. And this manufacturer is top-shelf, unlike what passes for overseas junk

https://www.amphenolrf.com/connectors/uhf.html

If you’re going to go back up on that tower, a better choice is “N” connectors. Weatherproof and 0.15 dB loss at 10 Ghz.

https://www.amphenolrf.com/connectors/n-type.html


#4

RG8 isn’t that low loss for the application because of the frequency.
I believe there have been discussions about which coax to use on this forum.

A datasheet i found states 15dB loss per 100m/300ft of cable at 900 MHz.
At 1100 MHz it’s even a little more, so you are looking at 5dB of loss for the 100 ft of cable.

Then the connectors someone mentioned also introduce loss.

Maybe get one of the LNAs that are available? Not sure how long they will last outside in Florida though.
This is one of them: https://www.amazon.com/Performance-Triple-Amplifier-RTL-SDR-Blog/dp/B078TBG4H8/ref=sr_1_2?ie=UTF8&qid=1537863268&sr=8-2&keywords=ads-b+lna

But it needs a bias-t power feed via the coax cable. So you either need a dongle that does it or a bias-t power feed.

May i ask how you installed the raspberry pi outside and what exactly went bad? (Just curious, not saying you did it wrong)


#5

Two things to check:

  1. If the N to SO-239 was added now, is it a 50 Ohms adapter? 50 and 75 Ohms N connector center pins have different dimensions.

  2. Switch to good and cheap RG6 cable. RG8 is not the best at 1090 MHz.


#6

@Dxista
RG6 is listed as 20dB/100m instead of 15dB/100m for RG8 (at around 1000MHz)

Don’t think it’s an improvement.


#7

At a 100 feet, RG6 is a little better than RG8. If the OP used RG8X, RG6 is even better.

With RG6 one can also use quad shield.


#8

I hate to suggest this but try another piece of coax to see if you have water infiltration in the jacket. So if you are going to go the aggravation of putting up another single piece of coax, purchase a piece with factory ends installed
I think getting higher and better ends (no conversions) would offset the longer run DB loss.
Did you say if you were offset (standing off) from the tower? If not you should as the metal tower might have adverse effect on signal especially if you are blocking your best direction. Make sure the cable does not touch the earth and remove lightning protection at least as a test.


#9

SO239 has no place in this setup. Remove them.


#10

Is this correct? Never heard of quad shield RG8.

One more reason to switch to RG6. F connectors, with all its simplicity, are still better than SO239.


#11

Nope, I was thinking 6. Whoops.


#12

If I understand , you have effectively doubled your coax loss and added another connector in the antenna feed line. I get the sense you already know that is not a good thing in itself, but that configuration preserves the Pie, so to speak.

Only other thing I can think of aside from what folks have already suggested is to spend big bucks on a long LMR400 run to lower the coax loss and lose a few connectors by staying factory N connectors till the SMA jumper.

I’m in North Carolina, so this equation of height vs environment vs losses in cable runs pops up in my nightmares constantly. Compromises in any solution I come up with. :thinking:


#13

Filtered LNA and RG6 Weather Seal (outdoor use) cable should be fine.
Wrap antenna connections with self-fusing rubber tape.


#14

During 2013 and 2014, I did not have RPi, and my DVB-T was plugged into Windows Desktop. The antenna was located near a large window which had a good view. I had to run 45 feet of RG6 Coax between antenna and DVB-T/Desktop, which were in another room. The range was less than 100nm.

As the custom made 1090 MHz amplifiers were very costly at that time (Euro 100 and above), I used a low cost ($4) Satellite inLine amplifier RCA D903. It worked very good and improved my range to 200nm. The label on this amplifier mentions 950- 2050 MHz (Satellite TV L-Band) and is supposed to cut off signals outside this band.

I had to add two more items:

  • Bias T
  • DC blocker between Amp and Antenna

At that time I was more interested in DIY, so the BiasT, the DC blocker, and the Antenna were all DIY :slightly_smiling_face:

I have just now checked, and this amplifier with (newer appearance) is still available on ebay

US $2.99 + US $2.90 Standard Shipping within USA
US $2.99 + US $17.31 International Priority Shipping to Canada :slightly_frowning_face:

https://www.ebay.com/itm/RCA-In-line-satellite-amplifier/202407638576

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RCA_Amp_D903

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The write-up on photo below shows Amp #2 also exists somewhere in the line. Initially I have installed 2nd amp near biast, thinking “more is better”.
Later I discovered that 2nd amp caused overload of DVB-T, and removing it improved reception. :slightly_smiling_face:


#15

Do you mean DC blocker between dongle and bias-t?

Those selfbuilt antennas should not mind DC do they?


#16

It depends on the antenna. Loops and J Poles, for example, would be problematic.


#17

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No, between amplifier and antenna
.
.

The one in photo in above post did NOT present a DC short, and therefore DC Blocker was not provided.

When I made Franklin Dipole with impedance matching stub, the impedance matching stub presented a DC short, and I had to add a DC blocker.

The Franklin Dipole, the Biast, and the DC Blocker were all DIY.
.
Below are photos of my DIY DC Blocker and Bias T, using recycled TV Splitter :slightly_smiling_face:

My DIY DC Blocker - Ceramic Capacitor any value between 47 pF and 470 pF

DIY_DC_Blocker

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My DIY Bias T

DIY_BiasT_2


#18

The Pi, an old desktop power supply, and an additional cooling fan were mounted inside a Hoffman enclosure and mounted on the tower. Over time, the Florida air rusted anything not gold-plated and copper connections started to grow crystals. Basically the standard result for electronics living outdoors in FL.



#19

@abcd567

I would try this one:

It’s the one I bought some time ago. I guess I have to give it a try, once I receive the new power inserter.:wink:


#20

Nice job. Mother nature always win, I guess.:thinking: